Waste disposal continues to present design challenges to environmental engineers, government officials and manufacturers of products that may produce environmentally objectionable wastes. Many waste materials decompose and leach into regions of underlying soil. In many instances the leachate flows into underground aquifers, thereby contaminating drinking water and affecting soil at locations remote from the waste disposal site.
Environmental engineers continue to develop methods for treating waste materials, including recycling selected materials and/or subjecting certain waste materials to processes that will make them less objectionable. However, acceptable treatments do not exist for many common waste products. Furthermore, even treatable wastes may require large holding areas for waste material awaiting treatment.
Many new waste disposal sites are lined to contain the waste material and to prevent such material from leaching into underlying soil and aquifers. The typical prior art liner comprises several layers that are assembled in overlapping relationship by workers at the waste disposal site. The various layers of the prior art liner assembly may be formed in wide sheets that can be rolled and delivered to the waste disposal site for subsequent unrolling and installation. The installation typically will require the sheets to be disposed with a specified overlap between the side edges of adjacent sheets. The sheets then will be welded in overlapped relationship at the installation site by an appropriate application of heat and pressure.
Many waste disposal sites are excavated depressions to be filled with the waste. An example of such a waste disposal site is depicted schematically in FIG. 1 which shows a large depression 10 dug into the soil 12. The depression 10 is characterized by a generally horizontal bottom wall 14 and a plurality of sloped side walls 16. The prior art liner assembly is identified generally by the numeral 18. The liner assembly 18 completely covers the bottom wall 14 and the side walls 16 of the excavated depression 10, and extends into overlying relationship with the surface of the soil 12 surrounding the depression 10.
The prior art liner assembly 18 is subjected to loads that tend to cause the liner assembly 18 to slide downwardly along the sloped side walls 16 and toward the horizontal bottom wall 14 of the depression 10. Such shifting of the prior art liner assembly 18 can expose regions of the uncontaminated soil 12 to the environmental impact of the waste material 20 being deposited in the depression 10. To prevent this downward shifting of the prior art liner assembly 18, many waste disposal sites dig a large ditch 22 around the entire perimeter of the depression 10. The prior art liner assembly 18 is then extended sufficiently beyond the perimeter of the depression 10 to line both the depression 10 and the peripheral ditch 22. A clean fill material 24 is then deposited onto the portion of the prior art liner assembly 18 extending across the peripheral ditch 22. The forces exerted by the fill material 24 on the portion of the prior art liner assembly 18 in the peripheral ditch 22 is intended to prevent the prior art liner assembly 18 from sliding down into the depression 10 as the waste material 20 is being deposited therein. It will be appreciated that the digging and subsequent back filling of the peripheral retention ditch 22 can add significantly to the time and cost required to prepare the depression 10 for receiving the waste material 20. Additionally, the need to have the prior art liner assembly 18 extend well beyond the perimeter of the depression 10 substantially increases the amount of liner needed, and hence increases the total cost to line the depression 10.
As shown in FIG. 2, the prior art liner assembly 18 may comprise a bottom layer 26 defining a solid planar plastic sheet having opposed smooth surfaces. A meshed or webbed transmissive layer 28 may be disposed on the solid bottom layer 26 in the prior art liner assembly 18. In some prior art systems, the transmissive layer 28 will be defined by several discrete layers exhibiting different transmissivities. For example, a web or mesh with large aperture sizes may be disposed directly on the solid bottom layer 26, and a finer textile may be laid over the web or mesh material with relatively large aperture sizes. The transmissive layer 28 is intended to enable a gravitational flow of liquid waste or leachate to a testing or collection point in the depression 10. For example, some systems will merely want to collect the liquid flowing through the deposited waste 20 for appropriate handling at another location. Other prior art systems, however, may want to provide a substantially impermeable liner assembly and will employ a solid top layer 30 over the transmissive layer 28 as depicted in FIG. 2. Leak detection means in communication with the transmissive layer 30 may be employed to detect any leakage through the solid top layer 30. In all such prior art systems, efficient predictable flowing of liquids through the transmissive layer 28 is very important. Clogging or collapsing of flow paths through the transmissive layer 28 can prevent the early detection of environmentally harmful leaks.
The transmissive layer or layers 28 and any top layer 30 that may be present necessarily contributes to the material costs for the prior art system, and the installation time and costs as well. In particular, each of the transmissive layers 28 employed in the prior art system must be separately delivered to the dump site 10 for installation after the complete installation of the bottom layer 26. The various strips of sheet material comprising the transmissive layers 28 must be properly assembled to one another and fixed relative to the peripheral retention trench 22 to prevent the entire transmissive layer 28 from sliding toward the bottom wall 14 of the prior art dump site 10. The labor costs and time required for installation and quality control can be very substantial.
In view of the above, it is an object of the subject invention to provide an environmentally protective liner for waste disposal sites.
It is another object of the subject invention to provide a liner for waste disposal sites that can substantially reduce the installation time and overall system costs for environmentally protecting soil near the waste disposal site.
A further object of the subject invention is to provide an environmentally protective liner exhibiting a high degree of transmissivity for ensuring an efficient flow of liquid waste materials through the liner.
Still another object of the subject invention is to provide an environmentally protective liner for waste disposal sites that substantially reduces the area of liner materials required to safely protect the site.